1. Field of the Invention
The invention relates to a radiated sound reducing structure that reduces radiated sound generated in a pipe through which gas passes.
2. Description of the Related Art
Technology is known that reduces radiated sound in an exhaust system of an internal combustion engine by increasing the rigidity by using a multi-layered pipe for the exhaust passage, or damping exhaust vibration by interlaminar friction.
Japanese Patent Application Publication No. 2007-239465 (JP-A-2007-239465) (page 8, FIG, 1), for example, describes technology that reduces radiated sound by inhibiting vibration from being transmitted through a partition wall, that is formed by a lateral divider that divides the inside. of a shell of a muffler for a vehicle, by increasing the rigidity of the partition wall by using a reinforcing plate to make the partition wall a double partition wall.
Japanese Patent Application Publication No. 61-65982 (JP-A-61-65982) (page 3, FIG. 2), for example, describes technology that reduces radiated sound by making an exhaust pipe of an internal combustion engine a double pipe formed of an inner pipe and an outer pipe, and then creating a gap by interposing metal mesh between those. pipes. Also, Japanese Patent Application Publication No. 2007-154694 (JP-A-2007-154694) (pages 4 and 5, FIGS. 2 and 3), for example, achieves a sound reducing effect and a heat insulating effect by making an exhaust pipe of an internal combustion engine a double pipe formed of an inner pipe and an outer pipe, and then providing a space between the inner pipe and the outer pipe by forming protruding portions on the outer periphery of the inner pipe. In addition, thermal stress is mitigated by elastic deformation of the protruding portions.
With JP-A-2007-239465, the rigidity of the partition wall is increased by making the partition wall a double partition wall. However, with this method, multiple partition walls and reinforcing plates must be fixed inside the shell so the structure becomes complex and productivity is low. Moreover, the weight of the vehicle muffler increases, which is a disadvantage for making the vehicle lightweight.
With JP-A-61-65982, it is necessary to provide a gap by the metal mesh between the outer pipe and the inner pipe, so the productivity is low with this kind of complex triple layer structure. Moreover, the weight of the muffler increases, which is a disadvantage for making the vehicle lightweight.
With JP-A-2007-154694, the protruding portions of the inner pipe are in point contact with the inner surface of the outer pipe. Therefore, although this structure may be effective for preventing vibration from being transmitted from the rigid inner pipe to the rigid outer pipe by the flexible deformation of the protruding portions themselves, there is absolutely no vibration dampening effect from sliding between the inner pipe and the outer pipe. Therefore, a sufficient radiated sound reducing effect cannot be expected.